Iron Man, Captain America, Spider-Man and the rest of the Marvel superhero crew are back to take on their biggest threat so far: Thanos. The trailer, which debuted on "Good Morning America" Wednesday morning, provides the best look yet at Josh Brolin's comic book villian, who's been lurking in the background of the MCU since he first appeared in the "Avengers" post-credit scene.

"Avengers: Infinity War" is the culmination of everything that Marvel has been doing since Robert Downey Jr. debuted as Tony Stark in 2008's "Iron Man." The upcoming film will feature pretty much every hero to hit the big screen so far as they team up to try and take down Thanos before he destroys the universe.

According to the official synopsis, the "Infinity War" will be the "deadliest showdown" so far for the Avengers.

An unprecedented cinematic journey ten years in the making and spanning the entire Marvel Cinematic Universe, Marvel Studios’ AVENGERS: INFINITY WAR brings to the screen the ultimate, deadliest showdown of all time. The Avengers and their Super Hero allies must be willing to sacrifice all in an attempt to defeat the powerful Thanos before his blitz of devastation and ruin puts an end to the universe.

In addition to the return of Downey Jr. and Brolin, "Infinity War" will also feature appearances by several Marvel favorites including Thor (Chris Hemsworth), Black Widow (Scarlett Johansson), the Hulk (Mark Ruffalo), Loki (Tom Hiddleston), Spider-Man (Tom Holland), Dr. Strange (Benedict Cumberbatch), Black Panther (Chadwick Boseman), a bearded Captain America (Chris Evans) and a ton of other heroes. Plus, Chris Pratt's Star-Lord and the rest of the Guardians of the Galaxy will join in on the fun as well.